If you verified that your computers are online and in sync, but a file still isn't appearing where expected, then there may be an issue with the name of the file itself. Files with a bad filename can sync to dropbox.com, but might not appear in the Dropbox folder on your computer, or work properly on incompatible operating systems.

Reserved filenames in Windows

Windows has a set of reserved words that can’t be used as valid filenames. If you create and name a file or folder from dropbox.com or a non-Windows device that includes a reserved word, then the file will not sync to your Dropbox on Windows computers. For a complete list of reserved file names, please see the Naming Conventions section of Windows Developer Network.

Ignored files

Some small system files aren't synced over Dropbox. These include:

desktop.ini

thumbs.db

.ds_store

icon\r

.dropbox

.dropbox.attr

Max character length

If you're having trouble syncing files and your file name is over 260 characters, the easiest solution is to shorten the name of the original file.

Beginning characters on Mac and Linux

Files or folders that begin with a period (e.g. .myfile.doc) will sync properly to the Dropbox folder on your computer. However, Mac and Linux operating systems will regard filenames that begin with a period as system files and hide the files automatically. You won’t be able to see the files without modifying advanced settings on your computer. Instead, you can sign in to dropbox.com and rename the files or folders (e.g. _myfolder).

Trailing characters

Files and folders that end with periods (.) won't sync properly between operating systems. If a file ends in a period, like file.txt., the file won't sync and it will appear in bad files check.

Temporary files

When some applications (such as Microsoft Word, Excel, or PowerPoint) open a file, they will often save a temporary file in the same directory and name it in one of the following ways:

Name begins with ~$ (a tilde and dollar sign) or .~ (a period and tilde)

Name begins with a tilde and ends in .tmp, such as ~myfile.tmp

Dropbox doesn’t sync these temporary files on any operating system.

Metadata and resource forks

Avoid syncing files that use metadata (or resource forks), including Mac aliases or Windows shortcuts. These types of files typically only work on the operating systems they were created on.

Junction points

Dropbox will follow Windows junction points and sync the files or folders they link to. However, any changes to those files or folders made from the Windows operating system will not sync again until the Dropbox desktop app is restarted. To get around this, move the original folder to your Dropbox and add a junction point from its previous location to link to its new location in the Dropbox folder.

Reparse points

In some rare cases, Windows may append a certain type of extended attribute, called a reparse point, to files or folders. The Dropbox desktop app cannot sync files or folders with this attribute.

If you see a red "X" on files or folders, it’s possible the cause is a reparse points. To correct this for an individual file, create a new file of the same file type, then copy the contents of the file that can't be synced to this new one and save it. To correct this on a folder, create a new folder and then copy and paste the contents from the folder that can't be synced to this new one.

Note that you may have multiple files and folders with reparse points. If this is true, you’ll need to apply this workaround several times. If you continue experiencing this issue, contact Microsoft support for more help.

A warning regarding metadata and FAT32 drives

Some documents have file attributes, or xattrs, in data attached to the file. We call this data metadata. Operating systems use metadata in many different ways: storing the icon, labeling your documents, attaching information to the file, permissions, and so on. Dropbox supports xattrs on all platforms. However, thumb drives and portable drives that use the FAT32 file system do not support metadata. If your Dropbox folder is on a FAT32 drive, unfortunately it is impossible to retain metadata when the file is moved or renamed.

Monitoring more than 10,000 folders on Linux

The Linux version of the Dropbox desktop app is limited from monitoring more than 10,000 folders by default. Anything more than that is not watched and, therefore, ignored when syncing. There's an easy fix for this. Open a terminal and enter the following: